1. Field of Invention
This invention relates to hydrophilic polyether polyurethanes having improved strength, good adhesion to different substrates, solubility in basic media, enhanced washability and which dissolve in neutral to slightly basic media to produce low viscosity solutions. The polymers are specifically adapted for use as adhesives, coatings, films, cosmetic applications, electroconductive surgical pads, shaving preparations, body and facial hair removal products, and antifogging agents.
2. Description of the Related Art
U.S. Pat. Nos. 3,822,238 and 3,975,350 describe a class of hydrophilic polyurethane polymers which on contact with an aqueous medium, absorb water with concomitant formation of a stable, water-insoluble hydrogel. In the water-swollen state, these polyurethanes vary from gel-like to soft and pliable and in the dry state from soft to hard and machinable.
U.S. Pat. Nos. 4,156,066 and 4,156,067 relate to a polyether polyurethane which contains a lactone group in the backbone and the polymer is subsequently swelled in a polar solvent such as acetone. The lactone group is ring opened with caustic to obtain a polymer with a carboxyl group in the polymer chain. These polymers have high solubility in neutral to base solutions, improved washability with ammonia and amines.
U.S. Pat. No. 4,743,673 describes a polymer containing an ester group which is neutralized in order to convert the sodium salts to carboxylic acid groups. This patent teaches that since carboxyl groups decarboxylate isocyanates, and since existing acidic diols were expensive, that the acid should to be shielded as an ester group. This process is complicated, lengthy and tedious. The polymer is made in two steps and the solvent must be added during the reaction in order to drive the reaction to completion. Then the polymer must be saponified, dissolved and the mixture is refluxed at the boiling temperature of the solvent for up to 11 hours, in order to make a water insoluble polymer which dissolves in water upon the addition of ammonia. The resulting polymer comprises a linear polyester diol.
U.S. Pat. No. 3,412,054 teaches the reaction of 4 to about 15% 2,2-di(hydroxymethyl) alkanoic acid with an isocyanate in order to produce polymers which become water soluble upon reaction with ammonia or an amine to form a quaternary salt. This patent teaches that the carboxyl group in alkanoic acidic diols does not react significantly with isocyanates to hinder the introduction of carboxylic acid groups into the polymer chain. The quaternary salts provide many hydrophilic sites which renders the urethane polymer water compatible if not water-soluble.
U.S. Pat. No. 5,120,816 relates to high strength hydrophilic polyether-polyester polyurethanes prepared at water levels in the reaction mixture of about 1.0 to 2.5%. This patent teaches that high tear strength polyether polyurethanes are achieved with less than 1% water. The hydrophilic polymers described in this patent are insoluble in water and polar solvents.
The above-described prior art introduces the carboxylic group into the polymer chain by lengthy and complicated processing steps and obtains a soluble polymer by neutralizing the acid with a base. It is desirable to provide polymers having higher strength and higher molecular weight and enhanced solubility in neutral to slightly basic media than lactone polymers and ester polymers.